Tempe Town Lake HISTORICAL Weather Data & Analysis

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Historic Weather Data For Tempe Town Lake
First off, I want to say a special thanks to Nancy Selover, Asst. State Climatologist, Office of Climatology, Arizona State University. Without her, none of this data would be available.

Since I am new to the area, I started asking around about the weather patterns to see what the wind was like, when it blows and when it doesn't. My personal obvservations were that it seems to either be completely dead, or blowing like stink. Several other local sailors confirmed this and one in particular said that there was a dead spot in the wind at 10am -- Oh no!!!, I was grief struken becauase my favorite time to meet other puddle duckers was to race once a month on a Saturday, meet at 10am, go race for an hour, then have lunch and then go do other stuff for the rest of the day.

So I started asking around and someone suggested I go to Weather Underground to lookup weather stations locally. So I did that and first came across the weather station CW2582. I emailed them but they have only been up for part of 2004. So they pointed me to the weather station that was actually on the dam at Tempe Town lake.

Nancy responded to my email and since I am rather low tech and don't have very much data analysis capability, provided the weather data since 2001 in a text format that I could import into Excel. With brilliance of insight, she seperated the columns of year, date, time etc so that it would be very easy to sort the data and look at it in various ways once imported into Excel !!

Here is the weather data file in Excel 4.0 format.
The variables are:
T (temperature Celsius)
Td (Dew point Celsius)
WS (wind speed - mph)
WD (wind direction in compass degrees 0 = none, 360 = north, 90 = east, etc)
MaxGust (maximum wind gust - mph)
There are 5 data points per day: 10am, Noon, 2pm, 4pm, 6pm.

Average Windspeed Per Time Of Day
Ok, so first things first, lets see what the yearly average windspeed for each time of day is. I sorted the data by time of day, for all years, and then figured the average wind speed for that time.

Time Of Day	Avg Windspeed	Avg Max Gust
10am	4.8 mph	7.0 mph
Noon	4.7 mph	7.5 mph
2pm	5.7 mph	9.1 mph
4pm	6.6 mph	9.9 mph
6pm	6.6 mph	8.9 mph

There is a major problem with this analysis - the average windspeed for a day with a 20 mph winds, and 3 days of 0 wind, is 5 mph.

Most Data Points at 7+ mph, Per Month
Which month had the most time periods of wind speeds over 7 mph, and also over 15 mph? I sorted all of the data by wind speed, and deleted all of the hour entries that were 6.99 or less of wind. There are 7370 data points, and 2424 points had wind speeds over 7mph, so 32% of the time we have a good chance at getting some acceptable wind. Also I figured how many time points had winds over 15mph, and that was 292 time points, so there is a 3% chance you are going to have wind a bit higher than most like to handle.

Month	7+ mph	15+ mph
January	154	9
February	181	20
March	209	26
April	247	55
May	245	45
June	306	34
July	254	31
August	210	12
September	197	20
October	141	9
November	157	19
December	134	17

So... it looks like June has the most wind.

7+ mph Windspeed Per Hour
Getting up early on Saturday and going sailing has always been a favorite time for me to go sailing. So to figure the percentage chance I have of sailing in 7mph+ winds, I deleted everything except the data at each hour, ending up with 1474 data points per hour. This is not segregated by month.
At 10am, only 368 had wind speeds over 7mph, so at 10am, you only have a 24% chance of good sailing wind.
At NOON, there were only 393 data points with 7mph or greater, making it 22% chance of good wind.
Later in the afternoon at 6pm, there were 649 data points over 7mph, making it a 44% chance of good wind.
So it looks like I should probably switch to sailing in the evenings.

Emory Heisler of the Arizona Yacht Club ran the data and sorted results by hour, subtotaled for each month.

Month	Avg Windspeed	MaxGust
Jan	4.52	6.16
Feb	4.34	6.22
Mar	5.38	6.52
Apr	5.46	6.23
May	5.11	6.11
Jun	4.00	5.87
Jul	3.80	5.46
Aug	4.38	5.08
Sep	5.08	5.85
Oct	4.06	5.17
Nov	3.61	6.44
Dec	3.14	5.51
7am average	4.40	5.88
Jan	4.44	6.18
Feb	4.27	6.04
Mar	5.97	7.51
Apr	6.06	6.97
May	5.28	6.55
Jun	4.22	5.73
Jul	4.13	5.57
Aug	4.88	5.63
Sep	6.11	6.97
Oct	4.95	5.90
Nov	4.20	7.15
Dec	3.76	6.01
8am average	4.84	6.33
Jan	5.33	7.35
Feb	5.08	7.27
Mar	6.43	8.20
Apr	6.18	7.15
May	4.38	5.95
Jun	3.58	5.13
Jul	3.79	5.58
Aug	4.84	5.85
Sep	6.29	7.41
Oct	5.13	6.40
Nov	4.73	8.41
Dec	4.49	6.97
9am average	4.99	6.77
Jan	5.58	8.12
Feb	5.82	8.48
Mar	6.31	8.76
Apr	5.33	7.29
May	4.09	5.94
Jun	3.59	5.86
Jul	3.60	5.53
Aug	3.85	5.54
Sep	5.64	7.18
Oct	4.71	6.05
Nov	5.47	9.02
Dec	4.67	7.46
10am Average	4.85	7.06
Jan	5.17	7.63
Feb	5.55	8.51
Mar	4.79	7.72
Apr	5.72	8.67
May	4.43	7.33
Jun	4.37	7.18
Jul	4.65	7.35
Aug	4.10	6.50
Sep	4.69	7.30
Oct	3.50	5.79
Nov	4.98	8.85
Dec	4.78	7.91
Noon Average	4.71	7.54
Jan	4.86	7.69
Feb	5.66	8.97
Mar	5.52	9.05
Apr	7.55	11.61
May	6.53	10.58
Jun	6.66	10.51
Jul	7.05	10.44
Aug	5.85	8.74
Sep	5.31	8.71
Oct	4.58	7.40
Nov	4.44	8.31
Dec	4.52	7.82
2pm Average	5.72	9.17
Jan	5.12	7.81
Feb	5.61	8.77
Mar	6.25	9.59
Apr	8.57	12.51
May	8.15	11.97
Jun	8.68	12.59
Jul	8.32	11.44
Aug	6.89	10.06
Sep	6.37	9.62
Oct	5.30	8.18
Nov	4.94	8.38
Dec	4.72	7.60
4pm Average	6.61	9.92
Jan	3.56	5.45
Feb	5.34	7.28
Mar	7.10	9.51
Apr	9.00	11.43
May	9.96	12.74
Jun	10.57	13.44
Jul	8.75	10.73
Aug	7.86	9.85
Sep	6.50	8.48
Oct	4.65	6.14
Nov	3.60	6.39
Dec	2.54	5.02
6pm Average	6.69	8.95
Grand Average	5.72	8.53

Your Data Analysis
Please feel free to download the weather data file and try to analyze it. If you see anything that is interesting, please email me with what you find and I'd be glad to post up the info here.

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